test for phase sequence

[lfcsparkycus]

done c & g 2330 level 2 & 3 and 2382. i wanna do 2391 or the new 1 (whatever that is) but have little practical experience, im not a stupid person but i dont see myself as qualified yet. do think i will know enough to pass if i read gn3 for a couple of months before i book up? real reason for this ramble is how do you test for phase sequence?

 

[telectrix]

with a phase sequence tester. some MFTs have them built in.

 

[lfcsparkycus]

would you connect the tester to all 3 phases at the same time hit the button and it will tell you if you have the correct sequence?

 

[ringer]

There is no correct sequence. You just need to make sure that all DBs and machines fed from the same supply have the SAME sequence. Is particularly important for rotating machinery.

 

[telectrix]

yes you do... copied from manual for my old tester
Determine Phase Rotation Direction
1. Connect the supplied color-coded test leads to the meter’s test
lead input jacks at the top of the meter.
2. Connect the test probes to the three mains phases for the system
under test.
3. L1, L2, and L3 indicators will illuminate one at a time on the
meter’s LCD display as each phase is connected.
4. The clockwise and counter-clockwise arrows with the left/right ‘L’
or ‘R’ icons display the phase rotation direction of the device
under test.
5. The sequence grid simply shows the three line sequences for
Clockwise ‘R’ and the three line sequences for Counter-Clockwise
‘L’.
Note: The rotational arrow indicators illuminate even if one of the test
probes is connected to a neutral or ground conductor instead of one
of the mains phases.

 

[telectrix]

as ringer says. if a motor goes the wrong way, then the phase rotation is incorrect for that situation

 

[needasparks]

As above but my fluke says 123 when correct and 321 when reversed.

 

[telectrix]

mine says red/yellow/blue. i've been trying for ages to get brown/black/grey LEDs but nobody makes them.

 

[pmac10]

would have to disagree with that statement Ringer, if a machine manufacturer states U1 to be connected to L1 etc if all the dbs are connected wrongly that motor or whatever will turn in the opposite direction, if the control circuit is protected with a phase sequence/rotation relay and all the dbs are connected the same but wrong, nothing will happen.

 

[needasparks]

mine says red/yellow/blue. i've been trying for ages to get brown/black/grey LEDs but nobody makes them.

Is that a metric red/yellow/blue or the old money imperial £/S/d

 

[lfcsparkycus]

cheers for your input guys and for clearing it up for me. im obviously not clued up enough yet but i"ll get there. thanks

 

[telectrix]

what's metric? is it an underground railway?

 

[telectrix]

cheers for your input guys and for clearing it up for me. im obviously not clued up enough yet but i"ll get there. thanks

yre clued up enough to ask what you don't know. that's how we all learn.

 

[needasparks]

It is interesting to have the new tickbox on the certs as I had a factory the the board had connected wrongly so every machine had to be reversed which made alterations a nightmare when some items really did need reversing on supply, I phoned DNO and they could not be bothered about it and would not come out to change back. I would have done it myself but it was a 400A intake so was on CT so not so straight forward.

 

[Engineer54]

There is no correct sequence. You just need to make sure that all DBs and machines fed from the same supply have the SAME sequence. Is particularly important for rotating machinery.

That's not always correct. There are many industrial situations where the correct phase sequence needs to be maintained from the main Switchboard to any point in the factory. usually all the 3 phase distribution circuit conductors are colour coded and so easy to keep in sequence. Where they are not, maybe in later bought-in multi phase panels, it's necessary to test and permanently mark up the correct sequence. A normal phase sequence tester will not always show correct sequence, L1, L2, L3 only that the phases are in sequence which could be L3, L2, L1. I have a rather expensive phase sequence tester, that will only indicate correct sequence when the correct probes are on L1, L2, L3, but not on L3, L2, L1 (if you get my meaning lol!!)

It's not uncommon at all, to see the old Blue conductor to be connected to L1, Yellow to L2, and Red to L3. A motor will still run in the correct rotation, it's just not in sequence with the phases from the origin. Some factory processes or rather the equipment /machinery just require that correct phase sequence L1/2/3 to be present at all it's interlinked connection terminals...